1. Field of the Invention
The present invention relates to the construction and installation of a drilling template for use in drilling subsea wells.
2. Description of the Prior Art
Often offshore oil and gas fields are developed by drilling a multitude of wells from a single offshore platform or drilling vessel. The position at which each of the wells penetrate the ocean floor is typically determined through use of a template which is a frame-like structure having a plurality of drilling guide collars, each of which corresponds to a future well location.
It is important that such drilling templates be oriented in a substantially level position. This is often difficult when the surface of the ocean floor itself is sloped.
One solution to the use of drilling templates on a sloped ocean floor is to construct the template so that its bottom surface is sloped similarly to the ocean floor. Such a template is shown for example in U.S. Pat. No. 4,784,527 to Hunter et al. The Hunter et al. template framework is placed on the ocean floor and then anchoring piles are inserted through the template. Subsequently, modular drilling templates are lowered into place within the main framework. The modular drilling templates include the guide collars for actual drilling of wells.
It is also known to place a drilling template on a plurality of preset anchor pilings. The difficulty with these systems is the subsequent leveling of the template upon the pilings. For example, U.S. Pat. No. 4,212,562 to Stone et al. discloses a template which is set in place on a plurality of pilings and then subsequently leveled with a complex hydraulic elevating mechanism. Once appropriately positioned, the template is clamped to the pilings by a hydraulic clamping mechanism. A somewhat similar proposal is seen in U.S. Pat. No. 4,674,920 to Regan et al.
It is also known to set a drilling template on a single wellhead, where the template rests on the upper end of the wellhead. This is shown for example in U.S. Pat. No. 4,706,757 to Harrington. Another similar system is seen in U.S. Pat. No. 4,497,592 to Lawson. These systems which set on a single wellhead or piling typically are relatively small templates.
There is a need for an economical, easily installed system for locating a relatively large drilling template in a level position upon an unlevel ocean floor without the need for complex adjusting mechanisms.